Treatment of phosphate-rock.



EARL BISHOP, 0F PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 ARMOUR FERTILIZERWORKS, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TREATMENT OF PHOSPHATE-ROCK.

manages;

Specification of Letters Patent.

Patented Nov. "3, H3 16.

No Drawing. Application filed August 10, 1914, Serial No. 855,984.Renewed February 1, 1916. Serial I No. 75,624. v

To all whom it may concern:

Be it known that I, EARL S. BISHOP, a citizen of the United States,residing at No. 4179 Centre avenue, Pittsburgh, Allegheny county, Stateof Pennsylvania, have invented certain new and useful Improvements inTreatment of Phosphate-Rock; and I do hereby declare the following to bea full, clear, and exact description of the invention, such aswillenable others skilled in the art to which it appertains to make anduse the same.

The present invention relates to the treatment of rock containingtri-calcium phosphateand. commonly known as phosphate rock for thepurpose of rendering the insoluble tri-calcium phosphate available as aplant food, and is based upon the discovery that the insolubletri-calcium phosphate contained in the .rock may be so converted, whenassociated with a suitable proportion of silica by any chlorid whichwill form hydrochloric acid by reaction with silica in the presence ofsteam when the mixture is subjected to a sufliciently high temperature,in the presence of steam. According to the amount of chlorid employed,the resultant calcium phosphate product will be either citrate-solubleor water-soluble, that is to say, it will be either the di-calciumsaltor the mono-calcium salt, as the case may be. In the practice of theinvention, the phosphate rockis ground to a fine state of subdivision,say to such a state of sub-division that its particles will'pass throughan .80 mesh screen. It is also preferable to grind with the rock thesilica to be added, in order to obtain as homogeneous a mixture aspossible, it being understood, in this connection, that the silica maybe supplied in whole or in part from the silica content of the rock,which will sufiice, in some instances, to obviate the necessity ofadding a supplemental supply of silica. So, also, the particular chloridselected may likewise be ground together with the rock and silica,

' but, in most cases, it will be preferable to dissolve the chlorid inwater and to add the chlorid solution thus obtained, to :the groundmixture of rock and silica, so that the mixture will be correspondinglymoistened, thereby lessening the tendency to length of say dusting inthe rotary kiln in which the mlxture 1s to be subsequently heated. As atyplcal instance of the practice of the invention, it may be assumedthat the chlorid selected, for initiating the operation, is potassiumchlorid, and that with 100 parts by weight of the phosphate rock areassociated 20 parts by weight of potassium chlorid and 5 parts by weightof silica (in addition to the silica present in the rock, which isusually as high as at least 15% by weight). In fact, the mixture shouldbe so compounded, that there shall be a sufficient excess of silicapresent to insure, in the presence of steam, the conversion of all ofthe chlorid into a silicate and hydrochloric acid. It will, of course,be understood, as hereinbefore indicated, that, should the proportion ofsilica naturally present in the sired excess, it will be unnecessary tosupplement it by any further addition; in general, however, the rockwill not contain a sufficient quantity of silica for the purpose. Theground mixture of phosphate rock, silica, and chlorid (the latter havingpreferably been added in solution in water, in order to moisten themass) is then fed into a rotary inclined kiln, of the general typefamiliarly employed in the calcining of cement; that is to say, a kilnwhich may conveniently have an internal diameter of say 8 ft. and a 160ft., and internally fired. The mixture to be treated is supplied to thekiln at its upper end, and the kiln is heated by the combustion of fuel,such as gas, oil or powdered coal, supplied by an adequate air andgas-injecting burner, projected through the customary stationary hood atthe lower end of the kiln,the usual provision being made for. thedischarge of the treated material at the lower or exit end of the kilninto a collecting pit, through which and elsewhere in and about the hoodenters a sufficient quantity of secondary air to obtain practicallycomplete combustion of the rock be sufiicient to amply supply thedebelow the sintering temperature of the mass,

so that when the product issues from the kiln, it will be in a looselyfriable condition.

This is of particular importance for the reason that, should thetemperature rise to such a degree that the product would clinker, theexpense of subsequently grinding it to the desired 80 mesh finenesswhich is particularly appropriate to its use would be very considerablyincreased. Steam, preferably superheated, is likewise admitted through apipe located alongside of or'immediately beneath or above the gas andair burner, so that the steam joins the gaseous products of combustionand with them passes upward through the kiln, and is thus brought incontact with the incoming rock mixture.

In those instances where it is desired to obtain a citrate-solubleproduct, the operation may be expressed in terms of the followingequation In this product, it will 'be noted that in addition to thecitrate-soluble dicalcium .Salt, there is obtained potassium silicate,which is itself immediately available as a plant food, and also calciumsilicate, which will likewise eventually break down and supply afertilizing ingredient to the soil. Particularly, however, it will benoted, that the reaction supplies a quantity of hydrochloric acid, whichis made available, thereafter, in the further practice of the invention.To this end, the hydrochloric acid vapors may .be absorbed in watersupplied to the top of ,a tower and which trickles down in counter-flowto the uprising prodx chloric acid thus obtained may be added to thenext succeeding batch of ground rock and silica supplied to the kiln, inlieu of o supplying such batch with a solution of chlorid. Or,preferably, the hydrochloric acid vapors are absorbed directly in theintended fresh batch of ground rock and silica, by conveying the vaporsinto contact with the proposed fresh batch or charge in a suitable toweror other receptacle provided for that purpose. In either case, the

operation may proceed for the conversion of fresh charges or batches ofground rock 0 and silica, it being only necessary to supply,

from time to time, such additional quantity of chlorid as may benecessaryto make up mechanical losses of hydrochloric acid. Thus thehydrochloric acid supplied to the fresh batch or charge of ground rockand.

eaction silica, outside the furnace, will convert a portion of the rockinto citrate-soluble form, with the simultaneous production of calciumchlorid, according to the following equation Thereupon, when thisproduct is subjected to treatment in the rotary kiln, the conversion ofthe remainder of the rock into a citrate-soluble form will proceed inaccordance with the following equation may be added to each batchtreated'so as to supply the desired quantity of alkali for theparticular use intended, and, of course, in this connection, it is to benoted that the initial operation represented by equation (1), gives aproduct having an alkaline reaction and is itself representative of thecapabilities of the process in this regard. In all cases, the product isnon-acid with espect to litmus and other common indicators and will notinjure the hands of the user and will not rot the bags in which it iscon tained, and it is likewise not hygroscopic to any marked degree. I

Whenever it is desired to produce the mono-calcium or water-solublesalt, this may be accomplished by proportionately increasing thequantity of chlorid and of silica, according to the following typical Itwill be noted that, inthis latter instance, the amount of hydrochloricacid produced, .is likewise double, and, consequently,

that there is a proportionately larger possible factor of mechanicalloss 1n hydrochloric Referring generallyxto the recess hereinbeforedescribed, it may be urther noted that there is special advantage inabsorbing the hydrochloric acid vapors within the fresh batch of groundrock and silica, for

the reason that it is found that in such case, the batch is agglomeratedinto lumps varying in size from about the size of a pea to about thesize of an egg, when it is withdrawn from the absorption tower orreceptacle, and, in this form, it is less liable to dusting thanotherwise. It may also be further pointed out as an advantage ofmamtaining the temperature of the kiln below the sintering temperaturefor the material treated that by so doing the amount of phosphoric acidvaporized from the kiln is considerably diminished. Such minor portionas may be driven off at a temperature below the sintering heat is,moreover, readily caught and recovered in the fresh batch of ground rockand silica and is thereafter returned with it into the process.

It will be further understood that any losses of hydrochloric acid may,of course, be supplied by corresponding additions of hydrochloric acidbut without the advantage in cheapness which is incident to supplyingsuch loss by the addition of chlorids.

lVhat I claim is:

1. The method of making phosphate rock available for plant food, whichcomprises subjecting to a sufficiently high temperature, in the presenceof steam, a mixture of the rock with a suitable metal chlorid and anexcess of silica sufiicient to combine with the metal of the chlorid andwith part of the calcium of the phosphate rock; substantially asdescribed.

2. The method of making phosphate rock available for plant food, whichcomprises subjecting to a sufliciently high temperature, in the presenceof steam, a mixture of the rock with a chlorid of a strong base and anexcess of silica sufficient to combine with the metal of the chlorid andwith part of the calcium of the phosphate rock; substantially asdescribed.

3. The method of making phosphate rock available for plant food, whichcomprises subjecting to a sufiiciently high temperature, in thepresenceof steam, a mixture of the rock with an alkali metal chlorid and anexcess of silica sufficient to combine with the metal of the chlorid andwith part of the calcium of the phosphate rock; substantially asdescribed.

4. The method of making phosphate rock available for plant food, whichcomprises rock with a metal chlorid and an excess of silica sufficientto combine with the metal of the chlorid and with part of the calcium ofthe phosphate rock, and recovering the hydrochloric acid given offduring the operation in a fresh batch of the mixture; substantially asdescribed.

6. A fertilizer comprising calcium acid phosphate in a soluble andcommercially available form, intimately associated with calcium silicateand an alkali silicate, said fertilizer resulting from the reaction uponphosphate rock at a high temperature of an alkali chlorid and asuificient excess of silica to combine with the metal of the chlorid andpart of the calcium of the phosphate rock, said fertilizer being freefrom uncombined acid, substantially non hygroscopic, and having analkaline reaction due to the alkali silicate; substantially asdescribed.

7. A fertilizer comprising calcium acid phosphate in a soluble andcommercially available form, intimately associated with calcium silicateand sodium silicate, said fertilizer resulting from the reaction uponphosphate rock at a high temperature of sodium chlorid and a suflicientexcess of silica to combine with the sodium of the chlorid and part ofthe calcium of the phosphate rock, said fertilizer being free fromuncombined acid, substantially non-hygroscopic, and having an alkalinereaction due to the sodium silicate; substantially as described.

In testimony whereof I aflix my signature, in presence of two witnesses.

EARL S. BISHOP.

Witnesses:

KENNETH R. PENNIE, M. A. BILL.

